It is standard in the production of trim or edge strips used in the manufacture of furniture to use a veined or marbleized synthetic-resin strand that is formed of two different resins that contrast somewhat and that are not completely mixed so that the resultant product has a surface on which the two resins are distinct. Such a resin workpiece can pass for a naturally occurring material but is of course much cheaper and also normally more durable than the material it is replacing.
A typical machine for making such a marbleized strand is seen in German patent 3,538,116 filed 26 Oct. 1985 and assigned to Rehau AG & Co. Here an extruder forces the hot liquefied matrix resin through an appropriately shaped die and the inlay resin is introduced into the extruder passage at the downstream end of the extruder worm. To mix the matrix and inlay resins the extruder worm is provided with radially projecting paddles or vanes. Thus the extent of veining or marbleizing is determined mainly by how fast the extruder worm is rotating. When it turns rapidly the veining is fine and when it turns slowly the veining is coarse.
It is also known from U.S. Pat. No. 4,834,639 to introduce the inlay or pattern resin into the worm so that it can exit therefrom into the matrix resin from holes in the worm. Once again the rotation rate of the worm determines the extent of mixing, although of course some minor effect on patterning can be achieved by varying the pressure with which the inlay resin is injected. The main disadvantage of such an arrangement is that the rotation rate of the worm also affects various other parameters such as the temperature of the matrix resin and the speed with which the matrix resin is moved. Thus when worm speed is adjusted to change the patterning, other unwanted effects are obtained.
The system of U.S. Pat. No. 4,921,414 of W. Schliehe et al has a nozzle which projects radially into the axial flow of matrix resin in the nozzle or die passage immediately downstream of the worm. The inlay resin is injected via this nozzle into the matrix-resin strand from a plurality of holes on the inlay nozzle that are directed to open downstream into the matrix-resin flow. Downstream of the inlay nozzle is a plate formed with a multiplicity of apertures that break up the combined inlay/matrix flow. Thus in this arrangement the only way to change the patterning of the inlay resin is to change the inlay nozzle and/or the aperture plate.